The present invention relates generally to high modulus/high strength fibers made from synthetic organic polymers, and more specifically to a method for making high modulus organic fibers having enhanced compressive strength.
High modulus, or high performance, polymeric fibers have increasingly been used to make high performance composites. Their very high strength-to-weight ratios makes them increasingly valuable, particularly for the aerospace industry.
Unfortunately, despite their very high tensile modulus and tensile strength, these high performance fibers are relatively weak in axial compression. This limits the compressive strength of composites made from them.
Aromatic heterocyclic polymeric fibers are made of even smaller fibers, called fibrils and microfibrils. One of the factors limiting the compressive strength of polymeric fibers is believed to be fibrillar and microfibrillar buckling under compression. Therefore, any reduction in fibrillar/microfibrillar buckling should result in fibers, and composites made from them, having enhanced compressive strength.
Proposed structural models in the prior art for existing carbon fibers having good physical properties in compression show a less highly ordered microfibrillar structure than in organic fibers. The microfibrils in the higher axial compressive strength carbon fibers appear to be entangled so that adjacent microfibrils support each other, thereby presumably reducing buckling and contributing to the desirable physical properties of the fibers in compression.
Thus it is seen that there is a need for a method for similarly entangling the fibrils and microfibrils of synthetic organic fibers to possibly improve their physical properties in compression.
It is, therefore, a principal object of the present invention to provide a method for making high performance polymeric fibers having an entangled microfibrillar morphology.
It is another principal object of the present invention to provide a method for making high performance polymeric fibers having enhanced axial compressive strength.
It is an object of the present invention to provide a method for making high performance polymeric fibers having fibrils and microfibrils resistant to buckling.
It is a feature of the present invention that it is a straightforward and uncomplicated adaptation of current methods for making high performance polymeric fibers.
It is an advantage of the present invention that it makes possible the use of organic polymeric fibers, with their corresponding other advantages, in new high-performance composites that previously were not practical because of insufficient compressive strength.
These and other objects, features and advantages of the present invention will become apparent as the description of certain representative embodiments proceeds.